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16. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon*, Hong-Kyu Kang, and Jeffrey I. Zink*
Spectroscopic Identification of Gas Phase Photofragments from Coordination Compound Chemical Vapor Deposition Precursors
Coord. Chem. Rev., 200, 1009-1032
 (Feb 24, 2000)
  DOI :

This review focuses on the gas phase photochemical fragmentation processes of coordination compounds that are precursors for the laser driven synthesis of solid-state materials such as thin films and nanoclusters from the gas phase. Specific emphasis is placed on the identification of photofragments by luminescence spectroscopy during the deposition process. In several cases, results from mass spectroscopy and from photofragmentation under the collision-free conditions of a molecular beam are included to clarify the identifications and mechanisms. Detailed experimental measurements have been made on metal diketonates, metal amides, metal xanthates and metal thiocarbamates. These compounds are useful as molecular precursors for the synthesis of thin films and nanoparticles of metals, binary and ternary materials, and semiconductor films.

15. [Evolutionary Nanomaterials & Nanodevices] Ana Acosta, Jeffrey I. Zink*, and Jinwoo Cheon
Ligand to Ligand Charge Transfer in (Hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I)
Inorg. Chem., 39 (3), 427-432
 (Feb 1, 2000)
  DOI :

Emission and UV−vis absorption spectra of (hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I), (CuTpAsPh3), (hydrotris(pyrazolyl)borato)(triethylamine)copper(I), (CuTpNEt3), and (hydrotris(pyrazolyl)borato)(triphenylphosphine)copper(I), (CuTpPPh3), are reported. The spectra of the arsine complex contain low-energy bands (with a band maximum at 16 500 cm-1 in emission and a weak shoulder centered at about 25 000 cm-1 in absorption) that are not present in the corresponding spectra of the amine or phosphine complexes. The lowest energy electronic transition is assigned to ligand to ligand charge transfer (LLCT) with some contribution from the metal. This assignment is consistent with PM3(tm) molecular orbital calculations that show the HOMO to consist primarily of π orbitals on the Tp ligand (with some metal orbital character) and the LUMO to be primarily antibonding orbitals on the AsPh3 ligand (also with some metal orbital character). The absorption shoulder shows a strong negative

14. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon and Jeffrey I. Zink*
In-Situ Gas-Phase Luminescence and Time-of-Flight Mass Spectroscopic Detection of Photofragments during Photochemical Synthesis of Copper Particles from Bis(tert-butylacetoacetato)copper
Inorg. Chem., 39 (3), 433-436
 (Feb 1, 2000)
  DOI :

During the 308 nm laser-driven photochemical synthesis of Cu particles from bis(tert-butylacetoacetato)copper, gas-phase photogenerated intermediates are identified by luminescence and time-of-flight mass spectroscopies. Pure Cu deposits are obtained as homogeneous, granular 200 nm particles. In the gas phase, luminescent photoproducts are observed and atomic Cu, Cu2, and dissociated ligand are identified spectroscopically. In addition, mass spectroscopy identifies Cu atoms, the dissociated ligand, a monoligated complex, and fragments of the ligands. The implications of the photofragmentation that produces copper atoms and dimers for the laser-assisted production of the Cu deposits are discussed.

13. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Peter Muraoka, and Jeffrey I. Zink*
Laser-Induced Deposition of Palladium and Gas-Phase Photofragmentation Pathways from (2-Methylallyl)(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) Palladium
Chem. Mater., 12 (2), 511-516
 (Feb 1, 2000)
  DOI :

Metallic palladium films are prepared at 10-2 Torr by 308 nm irradiation of gaseous (2-methylallyl)(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) palladium. Gas-phase luminescence spectra recorded during the photochemical deposition process are used to identify photofragments. X-ray photoelectron analysis of the films shows that they consist primarily of palladium metal; the films produced with H2 carrier gas have no detectable fluorine and barely discernible carbon contaminants. The Pd films are polycrystalline fcc (face-centered cubic) palladium with preferential growth along the 111 direction. Scanning electron microscopy shows that the films formed with H2 carrier gas are smooth and consist of granules less than 35 nm in diameter. Further characterization of the gas-phase photofragmentation process is carried out by time-of-flight mass spectroscopy. The dominant peak present in the mass spectrum under 308 nm irradiation arises from palladium ions. No fragments containing palladium and

12. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Matthew Guile, Peter Muraoka, and Jeffrey I. Zink*
Gas phase photoproduction of diatomic metal nitrides during metal nitride laser chemical vapor deposition
Inorg. Chem., 38 (9), 2238-2239
 (May 1, 1999)
  DOI :

Photolysis of M(NEt2)4 in the gas phase produces diatomic MN molecules (M = Ti, Zr, Hf). TiN and ZrN molecules were identified in the gas phase under CVD conditions by emission spectroscopy and time-of-flight mass spectroscopy. Nanostructured deposits of TiN were formed on quartz substrates by irradiating Ti(NEt2)4 gas at 355 nm. These studies demonstrate the gas phase formation of diatomic molecules having the same stoichiometry as that of the desired solid-phase deposit.

11. [Evolutionary Nanomaterials & Nanodevices] A. Stavrides, J. Ren, M. Ho, J. Cheon, J. Zink, H.P. Gillis*, and R.S. Williams
Growth and Characterization of Diamond-like Carbon Films by Pulsed Laser Deposition and Hydrogen Beam Treatment
Thin Solid Films, 335 (1-2), 27-31
 (Nov 19, 1998)
  DOI :

Amorphous diamond-like carbon films have been grown by pulsed laser deposition using a graphite target both with and without an atomic hydrogen beam incident on the growing film. Films grown with the hydrogen beam showed resistivity nearly two orders of magnitude higher than the films grown without hydrogen. Raman scattering confirmed a higher degree of sp3 bonding in films exposed to hydrogen atoms during growth. Films grown without hydrogen but exposed to the hydrogen beam after growth showed a significant increase in resistivity after exposure.

10. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, John E. Gozum, and Gregory S. Girolami*
Chemical Vapor Deposition of MoS2 and TiS2 Films From the Metal−Organic Precursors Mo(S-t-Bu)4 and Ti(S-t-Bu)4
Chem. Mater., 9 (8), 1847-1853
 (Aug 1, 1997)
  DOI :

The deposition of MoS2 and TiS2 thin films from the metal-organic precursors Mo(S-t-Bu)4 and Ti(S-t-Bu)4 has been investigated. Stoichiometric films with low levels of oxygen and carbon contaminants can be grown at temperatures between 110 and 350 °C and low pressure. The films are amorphous when grown at these low temperatures and have granular morphologies in which the grains are 30−90 nm in diameter, the larger grain sizes being observed at higher deposition temperatures. For the MoS2 deposits, the electrical conductivity was ∼1 Ω-1cm-1. For both precursors, the organic byproducts generated during deposition consist principally of isobutylene and tert-butylthiol; smaller amounts of hydrogen sulfide, isobutane, di-tert-butyl sulfide, and di-tert-butyl disulfide are also generated. A β-hydrogen abstraction/proton-transfer mechanism accounts for the distributions of the organic byproducts seen during the deposition of MoS2 and TiS2 films. Our results differ in some respects from those

9. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Deborah M. Rogers, and Gregory S. Girolami*
Mechanistic Studies of the Thermolysis of Tetraneopentyltitanium(IV). 1. Solution Evidence That Titanium Alkylidenes Activate Saturated Hydrocarbons
J. Am. Chem. Soc., 119 (29), 6804-6813
 (Jul 1, 1997)
  DOI :

Studies of the thermolysis of Ti(CH2CMe3)4 in solution have been carried out in parallel with studies of the chemical mechanism responsible for its conversion to titanium carbide under CVD conditions. In hydrocarbon solutions, the neopentyl complex thermolyzes to eliminate 2.1 equiv of neopentane as the principal organic product. A deuterium kinetic isotope effect (kα(H)/kα(D) = 5.2 ± 0.4) upon deuterating the alkyl groups at the α positions provides clear evidence that the initial step in the thermolysis is an α-hydrogen abstraction reaction to form neopentane. The activation parameters for this α-hydrogen abstraction process are ΔH⧧ = 21.5 ± 1.4 kcal/mol and ΔS⧧ = −16.6 ± 3.8 cal/(mol K). The titanium-containing product of this reaction is a titanium alkylidene, which in solution activates C−H bonds of both saturated and unsaturated hydrocarbon solvents such as benzene and cyclohexane. No activation of the C−F bonds of hexafluorobenzene is seen, however. Under special circumstances,

8. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Lawrence H. Dubois, and Gregory S. Girolami*
Mechanistic Studies of the Thermolysis of Tetraneopentyltitanium(IV). 2. Solid State and Ultra-High-Vacuum Studies of the Chemical Vapor Deposition of TiC Films
J. Am. Chem. Soc., 119 (29), 6814-6820
 (Jul 1, 1997)
  DOI :

The chemical pathway responsible for the conversion of the organotitanium compound tetraneopentyltitanium to titanium carbide has been studied under chemical vapor conditions and on single crystals in ultra-high vacuum. For every equivalent of TiNp4 consumed in the deposition process, 3.28 equiv of neopentane and 0.16 equiv of isobutane are produced; other organic species are also formed but in relatively small amounts. About 93% of the carbon and hydrogen originally present in the precursor can be accounted for in these products. Thermolysis of the specifically deuterated analogue Ti(CD2CMe3)4 yields a 2.25:1 ratio of neopentane-d3 and neopentane-d2; this result combined with a kinetic isotope effect of 4.9 at 385 K shows unequivocally that the first step in the deposition pathway under CVD conditions is α-hydrogen abstraction. The α-hydrogen abstraction step produces 1 equiv of neopentane and a titanium alkylidene, which undergoes further α- (and eventually γ-) hydrogen activation pr

7. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, David S. Talaga, and Jeffrey I. Zink*
Laser and Thermal Vapor Deposition of Metal Sulfide (NiS, PdS) Films and in Situ Gas-Phase Luminescence of Photofragments from M(S2COCHMe2)2
Chem. Mater., 9 (5), 1208–1212
 (May 15, 1997)
  DOI :

NiS and PdS thin films are prepared at 10-2 Torr from the single-source precursors M(S2COCHMe2)2, M = Ni and Pd. Two different vapor deposition processes, photochemical and thermal, are employed. Gas-phase emission spectroscopy is used during the photochemical deposition to identify the two elemental components of the final materials, the metal atom and sulfur, in the gas phase. NiS and PdS thin films are grown by the thermal process at 300 and 350 °C, respectively, on Si and quartz substrates. The NiS films are highly oriented rhombohedral (γ) phase, and the PdS films are tetragonal-phase polycrystalline. The metal sulfide films are grown photolytically by 308 nm laser irradiation of the gas-phase precursors at lower temperatures (near the sublimation temperature). The NiS films show no X-ray diffraction patterns, but the PdS films are polycrystalline tetragonal phase. The films are analyzed by various surface analytical tools including scanning electron microscopy, X-ray photoelectro


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